sequencer: rewrite update-refs as user edits todo list

An interactive rebase provides opportunities for the user to edit the
todo list. The --update-refs option initializes the list with some
'update-ref <ref>' steps, but the user could add these manually.
Further, the user could add or remove these steps during pauses in the
interactive rebase.

Add a new method, todo_list_filter_update_refs(), that scans a todo_list
and compares it to the stored update-refs file. There are two actions
that can happen at this point:

1. If a '<ref>/<before>/<after>' triple in the update-refs file does not
   have a matching 'update-ref <ref>' command in the todo-list _and_ the
   <after> value is the null OID, then remove that triple. Here, the
   user removed the 'update-ref <ref>' command before it was executed,
   since if it was executed then the <after> value would store the
   commit at that position.

2. If a 'update-ref <ref>' command in the todo-list does not have a
   matching '<ref>/<before>/<after>' triple in the update-refs file,
   then insert a new one. Store the <before> value to be the current
   OID pointed at by <ref>. This is handled inside of the
   init_update_ref_record() helper method.

We can test that this works by rewriting the todo-list several times in
the course of a rebase. Check that each ref is locked or unlocked for
updates after each todo-list update. We can also verify that the ref
update fails if a concurrent process updates one of the refs after the
rebase process records the "locked" ref location.

To help these tests, add a new 'set_replace_editor' helper that will
replace the todo-list with an exact file.

Reported-by: Phillip Wood <phillip.wood123@gmail.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/sequencer.h b/sequencer.h
index 8216b62..563fe59 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -133,6 +133,18 @@ void todo_list_release(struct todo_list *todo_list);
 const char *todo_item_get_arg(struct todo_list *todo_list,
 			      struct todo_item *item);
 
+/*
+ * Parse the update-refs file for the current rebase, then remove the
+ * refs that do not appear in the todo_list (and have not had updated
+ * values stored) and add refs that are in the todo_list but not
+ * represented in the update-refs file.
+ *
+ * If there are changes to the update-refs list, then write the new state
+ * to disk.
+ */
+void todo_list_filter_update_refs(struct repository *r,
+				  struct todo_list *todo_list);
+
 /* Call this to setup defaults before parsing command line options */
 void sequencer_init_config(struct replay_opts *opts);
 int sequencer_pick_revisions(struct repository *repo,